Exercise is an important part of any health plan and an excellent way of keeping your immune system in shape as well. While most people know that staying active is essential if you want to live a healthy life, starting an exercise routine can be daunting for anyone who's never done it and doesn't know what to expect.

With that in mind, here's a six-step plan that can help anyone start exercising, even if you never have before.

1. Realize the importance of physical exercise.

The first step is realizing just how important it is to get regular exercise. Regular exercise is vital to a healthy immune system. You must make regular exercise a top priority, especially as the seasons change and you're increasingly indoors, where germs are spread easily. Think of small ways to get more exercise into your daily routine. Even small choices, like taking the stairs instead of the elevator, can make a big difference.

2. Consult your physician.

If you aren't currently on a regular exercise program, get medical clearance if you have health problems or if you're over 40 years of age. See a physician if you have heart disease or high blood pressure. Also consult your doctor if, when exercising, you experience extreme breathlessness, pain or pressure in the chest, arm, teeth, jaw, or neck, or dizziness, fainting, or abnormal heart action (palpitations or irregular heartbeat).

3. Select an activity you can enjoy.

Next, select an activity that you enjoy -- such as bicycling, swimming, or racket sports. Make a commitment to do it daily for at least 20 minutes, preferably an hour. Make enjoyment your goal. Move your body enough to elevate your heart rate above its resting rate.

4. Monitor exercise intensity.

Exercise intensity is determined by measuring your heart rate (the number of times your heart beats per minute). While exercising, place the index and middle finger of one hand on the side of the neck just below the angle of the jaw or on the opposite wrist. Beginning with zero, count the number of heartbeats for six seconds. Simply add a zero to this number, and that's your pulse.

For example, if you counted 14 beats, your heart rate would be 140. Would this be a good number? It depends upon your "training zone." Your maximum training heart rate can be found simply by subtracting your age from 185. For example, if you are 40 years old your maximum heart rate would be 145. Your minimum training heart rate would be 20 less. In the case of a 40-year-old this would be 125.

So your training zone would be a heartbeat between 125 and 145 beats per minute. Having a heart rate of 140, then, would be pretty good -- you're working out at the upper end of your training zone. For maximum health benefits, stay in this range and never exceed it.

5. Do it often.

Exercise should be performed on a regular basis. A minimum of 15 to 20 minutes of exercising at your training heart rate at least three times a week is a necessity. Brisk walking (five miles an hour) for approximately 30 minutes may be the best form of exercise for weight loss, and the risks are extremely low.

6. Stay motivated.

Fire up your motivation by setting exercise goals, varying your routine, and keeping a record of your activities and progress. If at some point your enthusiasm wanes, skip one or two workouts. You'll come back later with an even stronger commitment.

Dr. Michael T. Murray is one of the world's leading authorities on natural medicine and the author of more than 30 bestselling books, including The Encyclopedia of Natural Medicine. He is a graduate and former faculty member, and serves on the Board of Regents, of Bastyr University in Seattle, Washington.